Cathode-ray tube



1940- P. S.'CHR|STALDI 2,225,099

CATHODE-RAY TUBE Filed June 10, 1939 2 Shets-Sheet 1 INVENTOR 1940- P.s. CHRISTALDI 2,225,099

CATHODE-RAY TUBE Filed June 10, 1939 2 Sheets-Sheet 2 INVENTOR 1 2/? J?(Z2! 04/! BY ,Betel' S- Christaldii v; Allen -B.-Du Mont As aresult of-1ievelopment of the so called Braun tube for television' reception, ithas-been I v r eral type disclosed in the patent -1 referred to.

As a result; the usesftowhich such'tubeseanbe definitely determined thatcertain valuesfwhether they be "of operatingpotentials orcertain-electrodes, or of dimensions in' the tube structure itself, mustbe properly correlated inorder to obtain the desired operatingaction.For example, it is known that byincreasing the operating potential on anaccelerating anode of a conventional cathode-ray tube, the intensityorbrightness of the traceor picture is increased.

A point or potential range' is finally reached, however, whereat thesensitivity of deflection is reduced a prohibitive amount, so that it isnotpractical tofurther increase the brightness of the picture'by thismethod alone. Another difilculty has been found to reside in the matterof main-,

taming the'scanning'electron ray at a good focus on the fluorescentscreen. *That is, in making certain chwang'es or variations in some ofF'the operating potentials or *in the structure of the tube itself tocorrect for or improve upon certain operating conditions, the result hasbeen to impair, at the same time, the operating action in other ways,suchas'by causing some formof distortion of the pattern or by causingsome degree 80- of defocusing of the-electronray-pn the fluores centscreen." Along with this development work,

the subject of electron opticshas beengiven considerable attention, inan attempt to formulate some working basis or formulae for use in :the"

85 most efficient design of cathode-ray tubes. for television reception."In putting this theoretical information to practice, however, it hasbeen found that there-are "still limitations in the way of'an occurringvdecreasegin eflicincy ofv opera- 40 tion of the tube'in one importantsense if certain changes are made-to'cause anincrease in eflic'iency of'operation of the tube .in another sense.-

-Many different types of cathode-ray tubes have been cons cted inywhichthere is postdefle'ction accel ration of "the electron beam. In most ofthese various constructions, however, an elaboratesystem .of electrodeshas been necessary which makes thesetubes impractical. so A simplifiedconstruction or system, employposed in proximity to the fluorescentscreen, is

disclosed-in Patent No. 2,186,635 issued January 9, 1940, to Allen l3.Du Mont and Alfred J. Hinck. so This novel ,coiistruzition makesfeasible cominvention; relates to improvementsfin; cathode-ray tubes oftheflgeneral type ftn ore-- particularly adapted for-televisionreceptioning a single electrode in the form of a ring disuction'pf cathode-raytubes having peiiating characterlstics referred to. v heimportanceof'electrode: posi v ids'i i s ap and nacinz 'orthe same, has beeoverlooked in cathode-ray'tubes of the gen- I 5 accelerationwpreeacceleration potential; I have found that unless'c'ertain designsare. ap- 15- plied, defocussing of thefiiiorescent' spotv occurs, I

distorting fields are set up, andit maybe-impos "sible to utilize morethan'thirty 'per lcent of'tlie e effective fluorescent screen area;

With the foregoing in mind, it "is one of these" objects of my inventinjtoprovlde an improved cdnstructionof cathode-ray tube of the chars,acter referred to in which the operating p'ote'n tials, anddiinensionsin the tube structure itself,

are such thatla picture of the desiredbrightness on the fluorescentscreen can be obtained'without' necessarily or unduly interfering with"the focus" or the sensitivity of deflection, Another object of myinvention resides in the provision of an improved constructionofcathode-, 3Q

"ray' tubeof 'thereharacter referred to, which has, advent gesfloverthose'proposedvheretoi'ore in the 7 way (if-{3i brighter or moreintensepicture on the fluorescent screen -forv similar operating 'condi- Itions, higher picture detail, and greater uni- .35

formity of'the pattern.

Another object of my invention resides in the provision of a simplifiedconstruction for, a cathode-ray tube in whichethere is post-deflectionacceleration of 'the electron beam or ray, and 40 "(which overcomes the;disadvantages and the limitations of the various designsproposed'heretofore. H Other objects and advantages will hereinafterappear.

5 v For the purpose of illustrating my invention, an 1 j embodimentthereof 15 shown in the drawings, wherein R 1 v Figure 1 is an enlarged,fragmentary, sectional view taken from Fig; 4, showing-details ofthe gunconstruction; 1 p Figs. 2 and 3 are views similar'to Fig. 1, show.- ingmodifications; =1 l Fig. 4 is af longitudinal, central sectional view ofa cathode-ray tube constructed and operating in accordance with myinvention;

Fig. 5 is a view similar to Fig. 1, showing a modification; and

Fig. 6 is an enlarged, sectional view, the Section being taken on theline 6-6 in Fig. 5.

The drawings show a cathode-ray tube having a gun construction similarto that described in the patent referred to. For convenience ofcomparison, the various parts have been designated by the same referencenumerals as the corresponding and respective parts in this pendingapplication.

with reference to Figs. 1 and 4, my improved.

cathode-ray tube comprises a tube l0 having a bulbous portion ii on theend wall of which is a fluorescent screen 3. In the neck portion l2 ofthe tube is the gun for developing the ray of electrons directed at andfocused on the screen.

The gun is supported from the stem i5 which is sealed to the open end ofthe neck l2, and comprises a cathode IS, a modulating electrode in whichthe cathode I6 is disposed, a first accelerating electrode 22 supportedfrom the stem by a lead wire 23, and a mica disc 24 supported from thestem by lead wires 25 and 28 which pass through the stem to the exteriorof the tube.

The gun comprises further a focusing electrode 23 supported by glassbeads from a second accelerating electrode 30 which in turn is supportedfrom a mica disc 32. Deflecting plates 33 are supported by the wiresshown from the mica disc 32. A second set of deflecting plates 36 issupported by the wires shown from the disc 32.

The first or preacceleratingeelectrode 22 above the modulating electrode20 is operated at the same voltage as the second accelerating electrode30. For this purp'ose, a connection 42 is made from the electrode 30 tothe lead wire 23. By applying a high voltage to the electrode 22, abrighter spot is obtained, and there is less tendency to defocus duringmodulation.

In my improved construction, there is a relatively large distance A fromthe tip 41 of the gun to the adjacent edges 43 of the second set ofdeflecting plates 36. The relation exists approximately, where A ismeasured in inches, C is the diameter in inches of the fluorescentscreen, and B is the distance in inches from the screen to the adjacentedges 43 of the flrst set of deflecting plates 33. Satisfactory resultshave been obtained by making A equal to .4 inch with C and B both 14inches. In the constructions used heretofore, the distance A is muchless. By making the distance A greater, and using the relation aboveexpressed, defocusing of the spot during deflection is eliminated. Thereason for this is that in my improved construction no appreciablebending or deflection of the beam or ray within the gun structure takesplace. Heretofore it has been generally supposed that no motion ordeflection of the ray occurs below the deflecting plates. Actually, thisis not true, and the motion of the ray in the gun during deflection hasbeen the cause of poor focusing in the prior constructions.

Important and novel characteristics of my improved tube reside in theprovision of the ring electrodes 58 and 53, whichmay be in the form ofsilver coatings on the inside surface of the tube i0, and in thedimensions and relations hereinafter specified. By this nieans, it ispossible with my improved tube to obtain a very intense trace 'orpicture by using an extremely high final accelerating voltage, butwithout, at the sametime, reducing the deflection sensitivity by about50%, when the final accelerating voltage is doubled, for example, aswould be the case in the various television receiver tubes usedheretofore. The reason for this is that in my improved tube thedeflection sensitivity is not an inverse function of final acceleratingvoltage or potential, as is the case in tubes of the prior art.

In the case of my improved tube, a potential of say 10,000 volts can beapplied to the top ring electrode 53, 5,000 volts to the electrode 30,and a 14-inch 9-inch tube tube Inches Inches Distance from edges 49 toscreen 9 16:3 13% Mean diameter of electrode 59 (E) 3 4 4 Mean diameterof electrode 58 1334 9% Distance from edge 60to edges 49 (2).. 1 1Diameter of screen 9 11% 8 Width of ring electrode 59 (Y) $4 In eithercase, Y may be made equal to Z.

In either case, with E from 2 to 4 inches, Z may be made from inch to 1inches.

The following voltages, measured with respect to cathode, have beenfound to give satisfactory results for the 14 inch tube.

Volts Grid (16) Preaccelerator (22) +5.000 First anode (29) +1,500Second anode (30) +5.000 Deflection plates +5,000:respective signalvoltages Ring electrode 58 440,000 Ring electrode 59 +5,000

The ring electrode 58 may be about one-quarter of an inch or more inwidth, and may be disposed a distance of about onehalf of an inch fromthe screen 3 or even about mid-way between the screen and the edge 60 ofelectrode 53.

It is possible with my improved tube, embodying the structural featuresand using the relations and values given above, to employ an extremelyhigh final accelerating voltage in order to get a very intense trace orpicture, and still deflect the ray to cause the same to scansubstantially the entire area of the screen3, since the deflectionsensitivity is only reduced by approximately 18%, as against aboutreduction in the cathode-ray tubes 'of the prior art, should the finalaccelerating voltage be doubled.

It has been found that when the distance from the edges 43 to the edgeis too great, electrostatic flelds are set up such that the useful areaof screen 3 is reduced as a strong function of the ratio of potentialson electrodes 58 and 53. In addition to the reduction of possible,effective On the other hand, when the distance from 49 to is too small,the electrostatic lines of force that would normally termi'nateinfl toproduce a spherical field within the intervening space, terminateinstead on the deflection plates 33 and, to some extent, on thedeflection plates 36. As a result, the accelerating fleld in that spaceis no longer spherical and produces a distortion of the fluorescentspot. Thus a normally round spot would become elliptical with its majoraxis parallel to the edges 49. e

Another important structural feature of my improvedtelevision receivertube resides in the provision of a conducting shield for collectingstray electrons which otherwise'would form or/set up a halo on thescreen 9 in the absence or presence of signal voltage. Such a'halo,whensignal is present, would reduce contrast. This shield also acts as a'light shield to prevent the heatercathodefrominterfering with thepicture. As shown-in Fig. 1, the shield may be-provided for by makingthe supporting mica disc 32 relatively thick to impart sufiicientrigidity, and of a large diameter so that its edge is in close proximityto the wall of the neck of the tube. On the cathode In this case, theshield has a third function,

which is that of shielding one set of plates from the other to reduceinteraction or coupling between the two orthogonal systems, whichinteraction would be seen as pattern distortion and/or defocusing of thetrace. The annular coating BI is electrically connected to the secondanode 30, as in Fig. 1.

It would also be possible to place the electron shield 32 beyond thedeflecting plates 33, or to associate it with the first or focusinganode. 29 as shown in Fig. 3. In the latter case, the shield wouldreplace and in addition serve the function of the supporting mica disc24 in Fig. 1. In the arrangement shown in Fig. 3, the shield would beconnected to the flrst anode 2.9 or to the lead wire 42 connecting tothe second anode 30.

For the purpose of making good contact between the second accelerationelectrode 30 and thering electrode 59, a spring connection element 64 isused. One end of this element contacts the electrode-59, the other end.being fixed to the gun structure, but insulated therefrom by a glasshead 65 and providedwith a coil spring .63. I

The element 64 is therefore spring-biased laterally outwardly withrespect to the gun ,to hold its 3 quency heating current used in.processing'the reason, a glass insulating bead is inserted in theelement 68, as shown. 7

In Fig. .5 a simplified construction is shown. 1

The elements 84a and 68a correspond to'and serve the same purposes asthe elements 64 and 33, respectively, in Fig. 1. However, the elements84a and 68a. are fastened to the holding straps I sibility of distortionof the pattern would be reduced.

ftube tends to burn these elements and the coat-1 I ing 59,.as a closedcircuit isformed. For this It will be understood that variousmodifications within the conception of those skilled in the art, I

of my invention or the scope of the claims;

I claim as my invention: v 1 In a cathode-ray tube, a tube having ascreen at the end wall thereof, a gun disposed in said tube fordeveloping a ray of electrons directed at and focused on said screen,means for deflecting said ray to cause the same to scan said screen andcomprising a first set of deflecting plates and a second set ofdeflecting pla'tesdisposed between said first set and the tip of saidgun, an electrode extending along said tube and beyond the outermostedges of said first set of plates in the direction toward said screen adistance in the range substantially from one-half inch to one andone-half inches, and a secondelectrode disposed between said screen andsaid first-named electrode, said second electrode oper-' ating atapotential positive with respect to the potential of operation ofsaidfirst-named electrode, the mean diameter of said flrst named electrodebeing in the range substantially from two inches to four inches.

2. In a cathode-ray tube, a tube having a screen at the end wallthereof, a gun disposed in said tube for developing a ray ofelectronsdirected at and focused on said screen, means for deflectingsaid ray to cause the same to scan said screen and comprising a firstsetv of deflecting plates and a second set .of deflecting platesdisposed between said first set and the tip of saidgun, an electrodeextending along said tube and beyond the outermost edges of said firstset of plates in the dlrectiontoward said'screen a distance ofsubstantially one inch, and a second electrode disposed between saidscreen and said first-named electrode, said second electrode operatingat a potential positive with respect to the potential of operation ofsaid first-named electrode, the mean diameter of said first-namedelectrode being in the range substantially from two inches to fourinches.

3. In a cathode-ray tube, a tube having a screen at the end wallthereof, a gun disposed in said tube for developing a ray of electronsdirected at and focused on said screen, means'for deflecting said ray tocause the same to scan said screen and comprising a first set of'deflecting plates and a second set of deflecting plates disposed betweensaid first set and the thief said gun, an electrode extending along saidtube and beyond the outermost edges of said first set of plates in thedirection toward said screen a distance in the range substantially-fromone-half inch to one and one-half inches, and a second electrodedisposed between said screen and said first-named electrode, said secondelectrode operating at a potential positive with respect to thepotential of operation of said first-named electrode, the mean diameterof said second electrode being greater than the effective diameter ofsaid screen by substantially two inches, the mean diameter of saidfirst-named electrode being in the range substantially from two inchesto four inches.

4. In a cathode-ray tube, a tube having a screen at the end wallthereof, a gun disposed in said tube for developing a ray of electronsdirected at and focused on said screen, means for deflecting said my tocause the same to scan said screen and comprising a first set ofdeflecting plates and a second set of deflecting plates disposed betweensaid first set and the tip of said gun, 'an electrode extending alongsaid tube and beyond the outermost edges of said first set of plates inthe direction toward said screen a distance in the range substantiallyfrom one-half inch to one and one-half inches, and asecond electrodedisposed between said screen and said first-named electrode said secondelectrode operating at a potential positive with respect to thepotential of operation of said first-named electrode, the distance fromthe tip of said gun to said screen being substantially seventeen inches,the diameter of said second electrode being substantially fourteeninches, the eflective diameter of said screen being substantially twelveinches, the mean diameter of said first-named electrode being in therange substantially from two 40 inches to four inches.

5. In a cathode-ray tube, a tube having a screen at the end wallthereof, a gun disposed in said tube for developing a ray of electronsdirected at and focused on said screen, means for deflecting said ray tocause the same to scan said screen and comprising a first set ofdeflecting plates and a second set of deflecting plates disposed betweensaid first set and the tip of said gun, an electrode extending alongsaid tube and beyond the outermost edges of said first set of plates inthe direction toward said screen a distance in the range substantiallyfrom one-half inch to one and one-half inches, and a second electrodedisposed between said screen and said first-named electrode, said secondelectrode operating at a potential positive with respect to thepotential of operation of said first-named electrode, the distance fromthe tip of said gun to said screen being substantially fourteen inches,the diameter of said second electrode being substantially ten inches,the efiective diameter of said screen being substantially eight inches,the mean diameter of said first-named electrode being in the rangesubstantially from two inches to four inches.

6. In a cathode-ray tube, a tube having a screen at the end wallthereof, a gun having a cathode and disposed in said tube for developinga ray of electrons directed at and focused on said screen, means fordeflecting said ray to cause the same to scan said screen and comprisinga first set 01' deflecting plates and a second set of deflecting platesdisposed between said first set and the tip of said gun, an electrodeextending along said tube and beyond the outermost edges of said firstset of plates in the direction toward said screen a distance in therange substantially from one-half inch to one and onehalf inches, and asecond electrode disposed between said screen and said first-namedelectrode, said second electrode operating at a potential positive withrespects to the potential of operation of said first-named electrode,the potential of said second electrode with respect to said cathodebeing substantially twice the potential of said first-named electrodewith respect to said cathode, the mean diameter of said first-namedelectrode being in the range substantially from two inches to fourinches.

7. In a cathode-ray tube, a tube having a screen at the end wallthereof, a gun having a first preacceierating anode and asecondaccelerating anode and disposed in said tube for developing a rayof electrons directed at and focused on said screen, means fordeflecting said ray to cause the same to scan. said screen andcomprising a first set of deflecting plates and a second set ofdeflecting plates disposed between said first set and said second anode,and a shield in the form of an electrically-conductive disc disposedbetween said second anode and said second set of plates with its edge inclose proximity to the wall of said tube, said shield being electrical-1y connected to one of said anodes.

8. In a. cathode-ray tube, a tube having a screen at the end wallthereof, a gun disposed in said tube for developing a ray of electronsdirected at and focused on said screen, means for deflecting said ray tocause the same to scan said screen, an electrode extending along saidtube and beyond said deflecting means in the direction toward .saidscreen, and a second electrode disposed between said screen and saidfirst-named electrode, said second electrode operating at a potentialpositive with respect to the potential of operation of said first-namedelectrode, the diaineter of said tube at a. plane in proximity to saidscreen being substantially greater than the maximum effective diameterof said screen.

9. In a cathode-ray tube, a tube having a screen at the end wallthereof, a gun disposed in said tube for developing a ray of electronsdirected at and focused on said screen, means for deflecting said ray tocause the same to scan said screen and comprising a first set ofdeflecting plates and a second set of deflecting plates disposed betweensaid first set and the tip of said gun, an electrode extending alongsaid tube and beyond the outermost edges of said first set of plates inthe direction toward said screen a distance in the range substantiallyfrom one-half inch to one and one-half inches, and a second electrodedisposed between said screen and said first-named electrode, said secondelectrode operating at a potential positivewith respect to the potentialof operation of said first-named electrode, the diameter of said tube ata plane in proximity to said screen being substantially greater than themaximum effective diameter of said screen, the mean diameter of saidfirstnamed electrode being in the range substantially from two inches tofour inches.

10. In a cathode-ray tube, a tube having a screen at the end wallthereof, a gun having a first preaccelerating anode and a secondaccelerating anode and disposed in said tube for developing a ray ofelectrons directed at and focused on said screen, means for deflectingsaid ray to cause the same to scan said screen and comprising a firstset of deflecting plates and a second Ill set of deflecting platesdisposed between said first set and said second anode, and a shield inthe forr'n of an electrically-conductive disc associated with the gunstructure and disposed with its edge in close proximity to the wall ofsaid tube, said shield being electrically connected to said secondanode.

11. In a cathode-ray tube, a tube having a screen at the end wallthereof, a gun disposed in said tube for developing a ray of electronsdirected at and focused on said screen and comprising a first set ofdeflecting plates and a second set of deflecting plates disposed betweensaid first set and the tip of said gun, an electrode extending alongsaid tube and beyond the outermost edges of said first set of plates inthe direction toward said screen, and a second electrode disposedbetween said screen and said firstnamed electrode, said second electrodeoperating at a potential positive with respect to the potential ofoperation of said first-named electrode, said tube being characterizedby the fact that the ratio of the mean diamet r, expressed in inches, ofsaid first-named elec rode to the distance, expressed in inches, fromsaid edges of said first set of plates to that edge of said first namedelectrode nearer said screen is in the range substantially from two tofour.

PETER S. CHRISTALDI.

